Solid structures in the form of wires, with a diameter of between a few nanometers and a few millimeters, may be developed by catalytic growth.
The Kolasinski document (Current Opinion in Solid State and Materials Science 10, 182-191 (2006)) describes various alternatives of this technology particularly in relation to:                catalytic growth mechanisms: vapor-liquid-solid, vapor-solid-solid, and solution-liquid-solid;        wire types: silicon, germanium, silicon-germanium, silica, alumina, type II-VI semi-conductors, type III-V semi-conductors etc.,        
The catalyst used generally comprises metal pads, made for example from copper, gold, platinum or aluminum, the size of which partly controls the diameter of the wires.
Thus, the nanowires, of silicon for example, are grown from a metal catalyst in drop form. By injecting a silicon carrier gas, the wire grows under the metal pad and draws it along with it. The catalyst drop thus remains at the apex of the wire and has then to be eliminated, particularly by etching.
Furthermore, when growing wires catalytically, metal catalyst residues may remain on the surface of the wires. This phenomenon is described, for example in the article by M. I. den Hertog et al. (Nano Letters 8, 1544-1550 (2008)), in the case of silicon wires developed by the vapor-liquid-solid mechanism with gold catalysis.
In fact, metal catalyst residues are harmful in respect of a large number of applications. For example, for silicon wires intended for uses in electronics or photovoltaics, the presence of metals such as gold or copper brings about significant deterioration in the performance of the devices, as these metals cause the appearance of deep electronic traps in the forbidden band of silicon.
A common solution for eliminating the metal catalyst residues on the surface of the wires comprises etching the metal, using a wet process or dry process, after growth of the wires.
However, eliminating metal catalyst residues by etching the metal is often of limited effectiveness. In particular, for wires comprising materials that are air oxidizable, as is the case with silicon, metal etching may become ineffectual through the formation, on the surface of the wire, of a layer of oxide.
There is therefore an obvious need to develop new technical solutions to eliminate the catalyst residues present on the surface, and particularly on the side, of solid structures in the form of wires developed by catalytic growth.